Hi all, Can anyone suggest how to go about debugging an issue involving bytes being dropped by the usbserial and serial8250 drivers? I have an i686 architecture machine running 2.6.35 that needs to speak to two different serial devices, one connected to the onboard 16550 and the other connected via USB to an FTDI chip. I am not using hardware flow control. Both devices drop bytes even at low bit rates (19200 on both ports). They do so in a somewhat predictable manner. On one of these ports all my program has to do is read a 65-byte packet each second, and what I see is that the packet almost always comes in at 64 bytes, sometimes 63. At first I suspected that a bug in my code was to blame, but I can see the same behavior by just running 'cat /dev/ttyUSB0 | hexdump -C'. Packets come in a single byte short, and then every 20 seconds or so I lose an additional byte. It's similar behavior for /dev/ttyS0, according to what I've seen in the logs written out by my program. The fact that two totally different drivers are involved makes me think maybe there is some other device driver that has a very long-running ISR? Just a guess- I'm not too familiar with such things. I read about a program called irqtune, which I thought about trying, but it looks like that is very old. By the way, some of the other device drivers in use on this system are: r8169, ath9k, snd_hda_intel (loaded but not used) and udlfb (DisplayLink framebuffer running xorg). The chipset is an 82801GBM and CPU is Intel Atom Diamondville. Nothing of interest from the kernel log. Oh, and, I don't know if this means anything, but I also experienced dropped packets a few months back, when I briefly decided to try switching from Ubuntu to plain Debian. The problem went away when I went back to Ubuntu. Even when I booted it up with the Debian kernel, which I thought was very strange. And now this problem is back. Back then it was with different hardware, although also Intel Atom. Suggestions appreciated very much. Thanks, Kyle -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
